Internal combustion engines whether gasoline or diesel, automotive, marine or stationary types rely on adequate lubricating oil supply for their operation. To monitor the level of lubricating oil in the sump of an internal combustion engine, a dipstick is used. This is manually withdrawn, wiped, reinserted withdrawn again and the wet line of the oil is observed.
As long as the wet line falls between a high level mark and a low level mark on the dipstick, the level is acceptable. When the oil level drops to the low level mark, the oil must be replenished.
Most internal combustion engines have an oil pressure switch which is activated when the oil level is low. Insufficient oil causes a low pressure and the switch provides a warning of this event. However, when this occurs the engine must be immediately stopped as the quantity of oil does not provide sufficient oil pressure to lubricate the engine.
The dipstick with a high mark and a low mark on it is the standard way to determine oil level in most vehicle engines and in marine engines. There is no automatic system available that indicates whether the oil level in the sump of an engine is at or below the low mark, between the low mark and the high mark or above the high mark.
Magnetically activated reed switches are known for determining liquid level. Some systems provide a continuous sensing level utilizing resistors and electronic circuits to provide a variable level indication.